1. Field of the Invention
The present invention relates to a signal processing module.
The present invention further relates to a navigation device provided with a signal processing module.
The present invention further relates to a vehicle provided with a navigation device.
The present invention further relates to a method of providing navigation data.
2. Related Art
Nowadays GPS navigation facilities are available that can relatively accurately determine a position of a vehicle. However, in some circumstances alternative navigation methods are required as GPS-navigation signals are not always available, for example at locations below sea level and in buildings. One such alternative method is based on data obtained from inertial sensors. Inertial sensors comprise gyroscopes and accelerometers. Gyroscopes provide information about the orientation of the vehicle and accelerometers provide information about its acceleration. If the initial position and velocity of a vehicle are known, its momentaneous velocity and position can be estimated by numerical integration of the acceleration and orientation data obtained from the accelerometers and gyroscopes. Generally accelerometers have a systematic error, also denoted as bias, resulting in a drift in position indication, exponential in time. Accordingly, such navigation systems based on inertial sensors need to be calibrated periodically to measure and compensate the sensor biases. With low-cost sensors, and without bias compensation, the navigation solution becomes useless within minutes.
A method to calculate a bias and a sensor signal compensated for bias is known as indexing. This method involves measuring acceleration at predetermined orientations, e.g. 0 and 180° of the acceleration sensor and calculating the bias from the sum of the measurement results. The estimation of the bias obtained in this way can be used to correct the measurement result. This has the disadvantage that the acceleration measurement has to be periodically interrupted for calibration. Alternatively a bias compensated acceleration signal may be obtained by subtraction of the measurement results. This has the disadvantage that it is necessary to wait until the sensor has rotated over 180 degrees before a new bias compensated acceleration signal sample is available.
U.S. Pat. No. 7,212,944 describes a method for determining bias comprising a plurality of sensors. Sequentially a different sensor is rotated, while the outputs of the other sensors are used to perform inertial calculations continuously through time. As each of the acceleration sensors is rotated from time to time, the effect of bias is averaged out. Although this allows for a continuous measurement of the acceleration, a relatively complex control of the acceleration sensors is required for sequentially rotating one of the sensors and for selecting the other sensors for determining the acceleration signal.
Accordingly there is a need for a more simple device and method to determine bias and/or to provide for a bias free estimation of the acceleration.